Stool Color Changes

Benjamin Wedro, MD, FACEP, FAAEM

Dr. Ben Wedro practices emergency medicine at Gundersen Clinic, a regional trauma center in La Crosse, Wisconsin. His background includes undergraduate and medical studies at the University of Alberta, a Family Practice internship at Queen's University in Kingston, Ontario and residency training in Emergency Medicine at the University of Oklahoma Health Sciences Center.

Definition of stool color changes

Stool, feces, or poop is the waste product of digestion. Food mixes with bile from the liver and digestive enzymes from the pancreas allowing protein, carbohydrates, and fats in the diet to be broken down to form a slurry. This liquid mixture passes through the small intestine where nutrients are absorbed into the blood stream and the liquid waste is delivered to the colon. In the colon, water is absorbed and stool is formed. Normal stool contains bacteria, digested food, cellulose from undigested plant material, and bile. The quality, quantity, and color of stool is an indicator of gastrointestinal health and changes may be significant.

What is the color of normal stool?

Stool (feces) color is most commonly brown. When stool color changes, often, an individual becomes concerned. The presence of the bilirubin (a breakdown product of blood) in bile is generally responsible for stool color. Bilirubin concentration can vary bile color from light yellow to almost black in color. Changes in bilirubin can cause stool to turn green, gray, or clay-like in color. Intestinal bleeding may turn stool black, tarry, red, maroon, or smelly stool. Medication and food may also affect stool color.

Most stool-to-stool changes in color have little meaning. However, some changes, particularly if the changes are consistent from stool-to-stool and not present in only one stool, can be important.

What are the causes of stool color changes?

Stool color changes are not always symptoms of disease in most cases. Changes in stool color may be due to:

Diarrhea may produce green stools caused by a number of reasons.

Abdominal pain may produce clay-colored stools.

Back pain may signal a tumor blocking the bile ducts.

Upper or lower abdominal pain (sometimes caused by bleeding in the GI tract.

Nausea and vomiting associated with stool color changes may be from heavy associated bleeding.

Green stools

If stool passes through the intestine too quickly, there might not be enough
time for bile to be digested and broken down to provide the normal brownish
stool color. Bile is a greenish brown fluid that is manufactured in the liver and
stored in the gallbladder. Bile helps digest fats in food. It takes time for the
bile to degrade and turn brown in the intestine and if the transit time is
short, the stool remains green colored. This is why diarrhea is often greenish
in color.

Green stools may be a normal variant. It can also be caused by a diet rich in
green vegetables, especially spinach. Iron supplements also may be a cause,
though it often turns stool black.

Rectal Bleeding (Blood in Stool, Hematochezia)

Causes of Blood in Stool

Blood in the stool can be bright red, maroon in color, black and tarry, or occult (not visible to the naked eye). Causes of blood in stool range from harmless, annoying conditions of the gastrointestinal tract such as hemorrhoids to serious conditions such as cancer.